High power and wide bandwidth RF power transistors and power amplifiers are important in wireless communication systems. Optimal design and performance of high power wideband power amplifiers require suitable transistor technologies such as high power density and low capacitance transistors. Gallium Nitride (GaN) on Silicon Carbide (SiC) power transistors are an example of suitable transistors offering very high power densities, high voltages, high impedances and excellent bandwidth. However, the higher power densities of such power transistors make heat removal more difficult relative to lower power density technologies where a greater cross sectional area is typically available for conduction. In addition, reduced cost, size and weight are very important for the advancement of modern wireless communication systems. As a result the high cost of high performance, high power density transistors (such as GaN on SiC) is undesirable; and considerable pressure exists to reduce the cost of such technology or substitute technologies.
Gallium Nitride (GaN) on Silicon is promising as an alternative due to a much more attractive cost structure. However Silicon has poor thermal conductivity relative to Silicon Carbide which results in higher thermal resistance, lower achievable power density and thus degraded performance and reduced bandwidth. In addition, the traditional packaging techniques for high power RF transistors involve heat conduction through a thinned substrate from the front or active side of the substrate where the transistors are formed to the opposite or back side of the substrate. The thinned substrate often contains through wafer vias for the required very low inductance grounding in common source and common emitter amplifier applications. The conduction of heat through the substrate results in an undesirable thermal resistance; and the use of a poor conductivity substrate such as Silicon makes this problem worse.